Estimate the % of Hypochlorite in Bleach Flashcards
What provides free chlorine in bleach?
ClO- that is chlorine which is available as an oxidising agent.
(It bleaches by oxidation)
What do you do to the bleach and why?
Dilute by a factor of ten as concentrated bleach can cause burns.
How do you carry out this titration?
Estimate the % of Hypochlorite in Bleach
Dilute by a factor of ten.
Pipette diluted bleach into the conical flask.
Add H2SO4.
Add 0.5 moles of Kl.
Brown colour of iodine appears.
Titrate with a standard solution of Na2S2O3.
As thiosulphate is added the brown colour fades.
When the solution is straw coloured add starch indicator.
Solution will turn blue.
Endpoint- solution turns colourless.
What indicator is used in this titration?
Estimate the % of hypochlorite in bleach
Starch indicator.
When is the indicator added and why?
When the solution is straw coloured to prevent the indicator from complexing with the iodine and ruining the result.
Describe how the sample of bleach was diluted.
Rinse pipette with deionised water.
Then rinse pipette with bleach.
Pipette bleach into volumetric flask.
Fill with deionised water until the calibration mark.
Read from the bottom of the meniscus at eye level.
Stopper and invert ten times
Why was KI (excess potassium iodide) used?
To form iodine by the reaction with OCL-.
Iodide ions help iodine dissolve.
What was the purpose of standing the conical flask on a white tile during the titrations?
To see the colour change more easily.
